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176 THE MARINE REVIEW REAR OF THE FORWARD END NEARLY ON ITS BEAM ENDS—THIS ILLUSTRATION SHOWS THE BULKHEAD TO KEEP THE WATER OUT OF THE HOLD cided that the changes in trim, due to the adding of the ballast, made the results obtained by such curves ex- ceedingly doubtful. Consequently, the more laborious method of calculating the angle of inclination, and trim resulting from the addition of each separate unit of fixed or water ballast was used. Bon Jean’s HOW THE AFTER SECTION APPEARED WHEN READY TO ROLL OVER TO curves were used to quickly get the de- sired displacement and trim. The weight was first considered as placed on the center line of the section in its correct fore-and-aft and_ ver- tical position and the cor- rect. :-draft: and. trim found. It was then considered as moved in AN ANGLE OF 90 DEGREES a transverse direction to its final po- sition. These figures were carefully checked several times as the calcu- lations were made. The turning moment of this weight, and the resisting moment of the ship for several angles, varying by 10 de- grees, was then calculated and curves drawn, the intersection of which gave the angle of inclination caused by the added weight. This was fairly satis- factory, but the results had to be modified and rechecked each time owing to the fact that in rolling over to a new angle the section was con- stantly changing trim. However, this work was the means of forming a complete mental picture of what was taking place and enabled the engineers to judge closely the action of the sec- tions, when they were finally turned. At about 40 degrees the curveg of in- clining moments ‘and resisting mo- ments failed to intersect, showing that a point of instability had been reached. This had been noted with the model. How Displacement Was Increased It was then decided to fill the for- ward port compartment of each sec- tion, and hold it full of water, until all the other tanks and pontoons were filled, and then pump this out. By doing this, the displacement was in- creased giving a much wider water plane, and consequent higher meta- center, and the center of gravity was lowered while at the same time the sections trimmed more evenly through- out the turning. Investigation showed that ballasted in this way, the sec- tions would always be ‘in stable equilibrium. The accompanying dia- gram has been prepated to slow graphically the shifting of the center of gravity and consequent resulting center of buoyancy and metacenter throughout the operation. The water lines shown are approximately a mean line for that inclination as to have attempted to show the trim at the same time would have — April, 1919 > Seite Sg rane eee